Facet mirrors are known from WO 2012/130768 A2. These facet mirrors are mirror arrays. These facet mirrors include a multiplicity of mirror elements in which the totality of the mirror elements forms a parqueting of a total reflection surface of the mirror array, and wherein the mirror array is embodied modularly as a tile element in such a way that the parqueting of the total reflection surface can be represented by a tiling of a plurality of such mirror arrays.
One problem of such facet mirrors is posed by a possibly non-reflective edge region of the mirror arrays. Such a non-reflective edge region may be desirable on account of the production method, on account of the electrical or other driving of the mirror arrays, or serve for the mechanical stability of the mirror array. Such a non-reflective edge region leads to shadings of the incident—“upstream”—and/or of the reflected—“downstream”—light. These shadings either result in a loss of light or an effective reduction of the reflectivity, which is undesirable particularly in the case of EUV lithography systems and arises from the fact that part of the incident light impinges on the non-reflective edge region and is therefore not reflected, or result in an enlargement of the volume of the envelope of the light-filled phase space, which can in turn have adverse effects on the uniformity of the field illumination and/or the homogeneity of the pupil filling. This volume enlargement arises as a result of the fact that the non-reflective edge regions have the effect that behind the mirror array—downstream—there are regions which are unilluminated on account of the shadings. These unilluminated regions can result in unilluminated pupil regions, whereby the pupil filling is adversely influenced, or the reticle field is not illuminated uniformly on account of the shadings.
Furthermore, WO 2009/132756 A1 discloses facet mirrors including macroscopic field facets which consist of one piece and which are combined with correction facets for correcting the uniformity of the field illumination. In this case, the correction facets, in accordance with one embodiment, can lie in the shading region of another facet mirror. In contrast to WO 2009/132756 A1, the shading region is avoided or greatly minimized in a targeted manner in the case of the present disclosure.
Furthermore, US 2009/0324170 A1 discloses stepped mirrors for reducing the coherence. The steps of such stepped mirrors introduce different phase shifts, whereby the coherence of the incident light is reduced.